Non-oriented electrical steel sheet and manufacturing method therefor

Abstract

A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, by wt%, 1.5-4.5% of Si, 0.1-2.0% of Al, 0.1-2.0% of Mn, 0.002-0.03% of at least one from among Mo, V and Nb, and the balance of Fe and inevitable impurities, and, in the steel sheet, among the total number of carbides, the proportion of the number of carbides having a particle diameter of 20 nm or more and including at least 5 wt% of at least one from among Mo, V and Nb is 0.2 or more.

Description

Non-oriented electrical steel sheet and manufacturing method thereof

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, wherein the thermal history of the steel sheet during cooling is appropriately controlled in an annealing process prior to cold rolling, thereby appropriately forming Mo, Nb, and V carbides within the steel sheet, thereby improving magnetism.

[0002] Non-oriented electrical steel is primarily used in motors that convert electrical energy into mechanical energy. This process requires excellent magnetic properties to achieve high efficiency. In particular, with the recent rise in eco-friendly vehicles powered by motors instead of internal combustion engines, demand for non-oriented electrical steel, used as a drive motor core material, is increasing. This demand is driven by the need for non-oriented electrical steel with both superior magnetic properties and strength.

[0003] The magnetic properties of non-oriented electrical steel are primarily assessed by core loss and magnetic flux density. Core loss refers to the energy loss occurring at a specific magnetic flux density and frequency, while magnetic flux density represents the degree of magnetization achieved under a specific magnetic field. Lower core loss allows for more energy-efficient motors under similar conditions, while higher flux density allows for smaller motors and reduced copper loss. Therefore, non-oriented electrical steel with low core loss and high flux density can be used to create drive motors with superior efficiency and torque, thereby improving the driving range and power output of eco-friendly vehicles.

[0004] The characteristics of non-oriented electrical steel sheets that must be considered also vary depending on the operating conditions of the motor. The general standard for evaluating the characteristics of non-oriented electrical steel sheets used in motors is widely used as W15 / 50, which is the iron loss when a 1.5T magnetic field is applied at a commercial frequency of 50Hz. However, in the case of non-oriented electrical steel sheets with a thickness of 0.35mm or less used in eco-friendly vehicle drive motors, magnetic characteristics are often important at low fields of 1.0T or less and high frequencies of 400Hz or higher, so W 10 / 400 The properties of non-oriented electrical steel sheets are often evaluated by iron loss.

[0005] A common method for improving the magnetic properties of non-oriented electrical steel is to add alloying elements such as Si, Al, and Mn. These alloying elements increase the steel's resistivity, reducing eddy current losses and lowering overall core loss. Furthermore, these alloying elements act as substitutional elements in the steel, strengthening it and increasing its strength. However, increasing the amount of Si, Al, and Mn alloying elements results in lower magnetic flux density and increased brittleness. Beyond a certain level, cold rolling becomes impossible, making commercial production impossible. In particular, thinner electrical steel sheets exhibit superior high-frequency core loss, but the resulting brittleness can be a critical issue. The maximum combined Si, Al, and Mn content for commercial production is known to be approximately 4.5 wt%. Optimizing the content of trace elements beyond this level can produce premium non-oriented electrical steel with superior magnetism and strength.

[0006] However, when high-resistivity alloying elements such as Si, Al, Mn, and Cr are added in large quantities, the problem of low magnetic flux density arises. In particular, the use of materials with high magnetic flux density is essential for materials requiring continuous weight reduction, such as eco-friendly electric vehicle drive motors.

[0007] To this end, a method for improving properties by thinning hot-rolled steel was proposed, and a method for improving magnetism by including high Al and performing double annealing and double rolling was proposed. In addition, a method for thinning hot-rolled steel using a thin slab manufacturing method was proposed.

[0008] However, the method of reducing the thickness of hot-rolled plate is difficult to mass-produce due to the increase in rolling load in the general hot-rolling process, and although some improvement in magnetism is confirmed through the addition of high Al and the two-time annealing and two-time rolling processes {110} <001> As the Goss aggregate structure also develops, the circumferential characteristics of the motor deteriorate and surface defects due to high Al addition also increase significantly.

[0009] One embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, by appropriately controlling the thermal history of the steel sheet during cooling in the annealing process prior to cold rolling, Mo, Nb, and V carbides are appropriately formed within the steel sheet, thereby improving magnetism, and a method for manufacturing the same are provided.

[0010] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%, the remainder being Fe and unavoidable impurities, and the number ratio of carbides having a particle size of 20 nm or more and containing at least one of Mo, V, and Nb at 5 wt% or more is 0.2 or more with respect to the total number of carbides in the steel sheet.

[0011] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0012] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge, and As.

[0013] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0014] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of B: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0015]

[0016] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: hot-rolling a slab containing, in wt%, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%, with the remainder including Fe and unavoidable impurities, to manufacture a hot-rolled steel sheet; a cold-rolling pre-annealing step of annealing the steel sheet; a cold-rolling step of cold-rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0017] The annealing step prior to cold rolling includes a step of cracking the steel sheet; a first cooling step of cooling the steel sheet to a first cooling temperature at a first cooling rate; and a second cooling step of cooling the steel sheet to a second cooling temperature at a second cooling rate that is 3 to 17°C / sec higher than the first cooling rate.

[0018] The slab may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0019] The slab may further contain 0.005 to 0.200 wt% of each or a combination of one or more of Sn, Sb, Bi, Pb, Ge and As.

[0020] The slab may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%).

[0021] The slab may further contain at least one of B: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), Co: 0.05 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0022] After manufacturing a hot-rolled steel sheet, subsequent steps can be performed while the scale remaining on the hot-rolled steel sheet remains.

[0023] A step of pre-cold rolling the hot-rolled sheet may be further included prior to the pre-cold rolling annealing step.

[0024] The reduction ratio in the preliminary cold rolling stage can be 65 to 80%.

[0025] The cracking temperature in the annealing step prior to cold rolling can be 800 to 1200°C.

[0026] The first cooling temperature may be 580 to 770°C.

[0027] The second cooling temperature may be 280 to 370°C.

[0028] The first cooling rate may be 5 to 20°C / sec, and the second cooling rate may be 10 to 30°C / sec.

[0029] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic flux density and iron loss.

[0030] A non-oriented electrical steel sheet according to one embodiment of the present invention has improved cold rolling properties, thereby improving productivity.

[0031] Ultimately, the non-oriented electrical steel sheet according to one embodiment of the present invention contributes to the manufacture of eco-friendly automobile motors, high-efficiency home appliance motors, and super-premium motor cores.

[0032] Figure 1 is a schematic diagram of the cooling pattern in the annealing stage prior to cold rolling.

[0033] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0035] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0036] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0037] In one embodiment of the present invention, the inclusion of additional elements means including the remaining iron (Fe) in an amount equivalent to the additional amount of the additional elements.

[0038] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0039] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0040]

[0041] A non-oriented electrical steel sheet according to one embodiment of the present invention includes, in wt%, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%, with the remainder being Fe and unavoidable impurities.

[0042] Below, the reasons for the limitation of the components of non-oriented electrical steel sheets are explained.

[0043]

[0044] Si: 1.5 to 4.5 wt%

[0045] Silicon (Si) increases the resistivity of the material, thereby reducing iron loss, and enhances strength through solid solution strengthening. If too little Si is added, the iron loss and strength improvement effects may be insufficient. If too much Si is added, the material becomes brittle, leading to a sharp decline in rolling productivity and the formation of a surface oxide layer and oxides that are detrimental to magnetism. Therefore, Si may be included in an amount of 1.5 to 4.5 wt%. More specifically, it may be included in an amount of 2.0 to 4.3 wt%. Even more specifically, it may be included in an amount of 2.5 to 4.0 wt%.

[0046]

[0047] Al: 0.1 to 2.0 wt%

[0048] Aluminum (Al) increases the resistivity of the material, thereby reducing iron loss, and enhances strength through solid solution strengthening. If too little Al is added, fine nitrides may form, making it difficult to achieve the effect of improving magnetism. If too much Al is added, excessive nitrides may form, deteriorating magnetism and causing problems in all processes, such as steelmaking and continuous casting, which can significantly reduce productivity. Therefore, Al may be included in an amount of 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.2 to 1.7 wt%. Even more specifically, it may be included in an amount of 0.5 to 1.6 wt%.

[0049]

[0050] Mn: 0.1 to 2.0 wt%

[0051] Manganese (Mn) improves iron loss by increasing the resistivity of the material and plays a role in forming sulfides. If too little Mn is added, fine sulfides are formed, causing magnetic deterioration, and if too much Mn is added, fine MnS is excessively precipitated and promotes the formation of {111} texture, which is unfavorable for magnetism, resulting in a rapid decrease in magnetic flux density. Therefore, Mn may be included in an amount of 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.3 to 1.8 wt%. More specifically, it may be included in an amount of 0.5 to 1.6 wt%.

[0052]

[0053] At least one of Mo, V, and Nb: 0.002 to 0.03 wt%

[0054] When molybdenum (Mo, vanadium (V), and niobium (Nb) are additionally added, they form carbides and complexly precipitate with TiC, thereby causing precipitate coarsening and reducing the number of fine carbides, thereby improving the magnetic flux density. If they are added appropriately, the aforementioned effect can be additionally obtained, but if they are included in too much, a lot of segregation may occur, which may inhibit grain growth and result in inferior magnetic flux density and iron loss. More specifically, at least one of Mo, V, and Nb may be included in an amount of 0.005 to 0.015 wt%. When Mo, V, and Nb are included singly, or when two or more are included, the combined amount may be included within the above-mentioned range. More specifically, at least two of Mo, V, and Nb may be included in a combined amount within the above-mentioned range. More specifically, Mo, V, and Nb may be included in a combined amount within the above-mentioned range. More specifically, Mo, V, and Nb may be included in an amount of 0.001 to 0.02 wt%, respectively. Can be.

[0055]

[0056] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0057] P: 0.1 wt% or less

[0058] Phosphorus (P) is a grain boundary segregation element that can improve magnetic flux density, but if added in too large a quantity, it increases the brittleness of the steel plate, resulting in poor weldability. More specifically, P may be included in an amount of 0.0001 to 0.0500 wt%.

[0059] C: 0.005 wt% or less

[0060] Carbon (C) can cause magnetic aging and combine with other impurity elements to form carbides, thereby hindering grain boundary or domain wall movement and deteriorating magnetic properties. More specifically, C can be included in an amount of 0.0001 to 0.003 wt%.

[0061] S: 0.005 wt% or less

[0062] Sulfur (S) can form fine precipitates, MnS and CuS, which can worsen magnetic properties and hot workability. More specifically, S can be included in an amount of 0.0001 to 0.0030 wt%.

[0063] Ti: 0.005 wt% or less

[0064] Titanium (Ti) can be limited because it forms carbonitrides and thus hinders domain movement. More specifically, Ti can be included in an amount of 0.0001 to 0.005 wt%. More specifically, Ti can be included in an amount of 0.0001 to 0.003 wt%.

[0065] N: 0.005 wt% or less

[0066] Nitrogen (N) not only forms fine AlN precipitates within the base material, but also combines with other impurities to form fine precipitates, thereby inhibiting grain growth and domain wall migration, thereby worsening iron loss. More specifically, N may be included in an amount of 0.0001 to 0.0030 wt%.

[0067]

[0068] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge, and As.

[0069] Sn and Sb

[0070] Tin (Sn) and antimony (Sb) play a role in suppressing the development of {111} orientation, which segregates at the grain boundary in the early stage of final recrystallization annealing and worsens magnetism. If too much Sn and Sb are added, the recovery and growth of coarse stretched band structure may be hindered and the surface quality may be deteriorated. Therefore, at least one of Sn and Sb may be further added within the above-mentioned range. More specifically, Sn may be included in an amount of 0.005 to 0.200 wt% or Sb may be included in an amount of 0.005 to 0.200 wt%.

[0071] Bi, Pb, Ge, and As

[0072] When added, bismuth (Bi), lead (Pb), germanium (Ge) and arsenic (As) segregate at grain boundaries, thereby relieving stress concentration at grain boundaries during cold rolling, and thus reducing stress concentration in the subsequent recrystallization annealing process. <111> / ND By suppressing the recrystallization of the grains, the magnetic flux density is improved. If these are added appropriately, the aforementioned effects can be additionally obtained. However, if they are included in excessive amounts, segregation may occur in large quantities, inhibiting grain growth and lowering the magnetic flux density and iron loss.

[0073]

[0074] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0075] Cu: 0.005 to 0.200 wt%

[0076] Copper (Cu) forms sulfides with manganese (Mn). If too little Cu is added, fine precipitation of (Cu · Mn)S may occur, degrading magnetism. If too much Cu is added, high-temperature embrittlement may occur, leading to cracks during rolling or hot rolling. More specifically, Cu may be included in an amount of 0.01 to 0.10 wt%.

[0077] Cr: 0.01 to 0.50 wt%

[0078] Chromium (Cr) increases resistivity and improves iron loss. If too little Cr is added, the resistivity-enhancing effect may not be sufficient. If too much Cr is added, the magnetic flux density may decrease. More specifically, Cr may be included in an amount of 0.050 to 0.20 wt%.

[0079] Ni: 0.05 wt% or less

[0080] Nickel (Ni) can react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetism. More specifically, it can contain 0.001 to 0.03 wt% of Ni.

[0081] Zn: 0.01 wt% or less

[0082] Zinc (Zn) can act as an impurity and degrade magnetism if the content is excessive. Therefore, Zn may be added further within the aforementioned range. More specifically, Zn may be included in an amount of 0.001 to 0.005 wt%.

[0083] Co: 0.05 wt% or less

[0084] Cobalt (Co) does not form fine precipitates that reduce the magnetism of steel sheets, but it can increase high-temperature strength and cause poor coil shape after hot rolling.

[0085]

[0086] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of B: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Zr: 0.0050 wt% or less (excluding 0%), Te: 0.0100 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0087] B: 0.0050 wt% or less

[0088] Excessive addition of boron (B) can cause deterioration of magnetism through the formation of inclusions in the steel. Therefore, B may be included in an amount of 0.005 wt% or less. The lower limit is not particularly limited, but may be 0.0001 wt% due to steelmaking costs. More specifically, B may be included in an amount of 0.0001 to 0.0030 wt%.

[0089] Ca: 0.0050 wt% or less

[0090] Calcium (Ca) has a strong tendency to form precipitates within the steel, and forms fine sulfides within the parent material, which inhibits grain growth and domain wall movement, thereby deteriorating iron loss.

[0091] Zr: 0.0050 wt% or less

[0092] Excessive addition of zirconium (Zr) can cause deterioration of magnetism through the formation of inclusions in the steel. Therefore, Zr can be included in an amount of 0.005 wt% or less. The lower limit is not particularly limited, but may be 0.0001 wt% due to steelmaking costs. That is, Zr can be included in an amount of 0.0001 to 0.0050 wt%. More specifically, it can be included in an amount of 0.0005 to 0.0030 wt%.

[0093] Te: 0.0100 wt% or less

[0094] Tellurium (Te) diffuses into the oxide layer on the surface of a hot-rolled coil, increases the coefficient of friction between the oxide layer and the rolling work rolls, and concentrates under the oxide layer to improve hardness. Therefore, it can be added to prevent the fractured oxide layer during rolling from being pressed into the base metal and to be removed. If the amount of Te added is too small, the effect may be minimal. If too much Te is added, the oxide layer is easily removed, and the base metal comes into direct contact with the work rolls, reducing the effect. In addition, deformation bands may be excessively generated in the steel sheet during cold rolling, which may lead to the development of a {111} / ND texture that is unfavorable for magnetism. More specifically, tellurium may be included in an amount of 0.0001 to 0.007 wt%.

[0095] Mg: 0.0050 wt% or less

[0096] Magnesium (Mg) is an element that mainly combines with sulfur to form sulfides, and can affect the surface oxide layer of the steel base. Therefore, Mg may be included in an amount of 0.0050 wt% or less. The lower limit is not particularly limited, but may be set to 0.0001 wt% due to steelmaking costs. That is, Mg may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, it may be included in an amount of 0.0005 to 0.0030 wt%.

[0097]

[0098] The remainder comprises iron (Fe) and unavoidable impurities. Unavoidable impurities are impurities mixed in during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets. Since these impurities are widely known in the art, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. When additional elements are included, they are included in place of the remainder, iron (Fe).

[0099]

[0100] As described above, in one embodiment of the present invention, by including appropriate amounts of Mo, V, and Nb, carbides are formed and coarsened by composite precipitation with TiC, etc., thereby reducing the number of fine carbides and improving the magnetic flux density. In one embodiment of the present invention, the number ratio of carbides having a particle size of 20 nm or more and containing at least one of Mo, V, and Nb in an amount of 5 wt% or more with respect to the total number of carbides in the steel sheet is 0.2 or more.

[0101] Carbide refers to a carbon component within a steel sheet that has aggregated and formed into a particle form. In other words, it refers to a portion containing carbon in greater quantities than the base material content of the steel sheet. In one embodiment of the present invention, carbide is determined to be a particle containing a carbon component and having a carbon agglomerate particle size of at least 1 nm when measured by TEM (Transmission Electron Microscopy) and EDS (Electrical Dispersive Spectroscopy). The measurement reference cross-section of the carbide is not particularly limited, but may be a normal plane (TD plane) in the rolling vertical direction (TD direction) of the steel sheet. The particle size of the carbide refers to the diameter of an imaginary circle having the same area as the area occupied by the carbide.

[0102] In one embodiment of the present invention, the ratio of the number of carbides having a particle size of 20 nm or more and containing at least one of Mo, V, and Nb in an amount of 5 wt% or more with respect to the total number of carbides in the steel sheet is 0.2 or more. If the particle size is too small or if there are many carbides such as TiC containing little Mo, V, and Nb, the movement of magnetic domains becomes difficult, which increases iron loss. When two or more types of Mo, V, and Nb are contained, it means that the combined amount is 5 wt% or more. More specifically, the ratio of the number of carbides having a particle size of 20 nm or more and containing at least one of Mo, V, and Nb in an amount of 5 wt% or more with respect to the total number of carbides in the steel sheet is 0.2 to 0.5. More specifically, it is 0.21 to 0.35. The ratio of carbides can be analyzed using an image analysis program on an image obtained through TEM or SEM and EDS. To reduce deviation according to the measurement location, the ratio can be obtained by measuring non-overlapping locations three or more times for a specimen of 20㎛×20㎛ or more and using the average value.

[0103] In one embodiment of the present invention, the density of the carbide is 2.5 / ㎛. 2 It can be below. If the density of carbide is high, even if the carbide ratio is high, the absolute number of fine carbides increases, which can have a negative effect on iron loss. More specifically, the density of carbide is 0.1 to 2.5 pieces / ㎛. 2 It can be. More specifically, 2.00 to 2.45 / ㎛ 2 It can be. The density of carbide can be obtained in the same way as the ratio of carbide mentioned above.

[0104] The size ratio and density of carbides can be controlled by the cooling pattern in the annealing stage prior to cold rolling, and the specific details are explained in relation to the manufacturing method of non-oriented electrical steel sheets.

[0105] In addition to C, the carbide may contain one or more of Ti, S, Cr, N, O, and Fe.

[0106] In one embodiment of the present invention, the magnetic flux density in the rolling direction is excellent and the high-frequency iron loss is excellent.

[0107] Specifically, a non-oriented electrical steel sheet according to an embodiment of the present invention can satisfy the following equation 1.

[0108] [Formula 1]

[0109] (B50 L + B50 C ) / 2 ≥1.60

[0110] (However, in Equation 1, B50 L is the magnetic flux density (B50, Tesla) measured in the rolling direction, and B50 C represents the magnetic flux density (B50, Tesla) measured in the vertical direction of the rolling.)

[0111] B50 refers to the magnetic flux density induced in a magnetic field of 5000 A / m.

[0112] Equation 1 is a general method for evaluating the magnetic flux density of a non-oriented electrical steel sheet, and means the average value of the magnetic flux density (B50) in the rolling direction (L) and the rolling vertical direction (C). More specifically, the value of Equation 1 can be 1.60 to 1.65.

[0113] In addition, a non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 2.

[0114] [Formula 2]

[0115] (W10 / 400 L + W10 / 400 C ) / 2 ≤ 6.885 × e (2.99×t)

[0116] (However, in Equation 2, W10 / 400 L is the iron loss (W10 / 400, W / kg) measured in the rolling direction, and W10 / 400 Cis the iron loss (W10 / 400, W / kg) measured in the vertical direction of rolling, e is a natural constant, and t represents the thickness (mm) of the electrical steel sheet.

[0117] W10 / 400 is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz.

[0118] Equation 2 can greatly reduce the iron loss by securing excellent magnetic flux density according to Equation 1, thereby increasing the efficiency of the motor. This iron loss characteristic is affected not only by the magnetic flux density characteristic, but also by the thickness of the steel plate. Therefore, it refers to the iron loss that can be secured in a steel plate that exhibits excellent magnetic flux density in the entire direction of the steel plate, as in the present invention, depending on the thickness of the steel plate. More specifically, W10 / 400 may be 13.5 W / kg or less. More specifically, it may be 12.5 to 13.4 W / kg. In this case, the thickness may be 0.25 mm.

[0119]

[0120] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a step of hot-rolling a slab to manufacture a hot-rolled steel sheet; a step of annealing the steel sheet before cold rolling; a step of cold-rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0121] Below, each step is explained in detail.

[0122] First, the slab is hot rolled.

[0123] The alloy composition of the slab has been described in the alloy composition of the previously mentioned non-oriented electrical steel sheet, so a duplicate description will be omitted. Since the alloy composition does not substantially change during the manufacturing process of the non-oriented electrical steel sheet, the alloy composition of the non-oriented electrical steel sheet and the slab are substantially identical.

[0124] Specifically, the slab contains, by weight %, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%, with the remainder being Fe and unavoidable impurities.

[0125] As other additional elements have been described in the alloy composition of non-oriented electrical steel sheets, redundant descriptions are omitted.

[0126] Slabs can be heated before hot rolling. The heating temperature of the slab is not limited, but the slab can be heated to 1200℃ or lower. If the slab heating temperature is too high, precipitates such as AlN and MnS present within the slab may be re-dissolved and then finely precipitated during hot rolling and annealing, inhibiting grain growth and reducing magnetism.

[0127] Next, the slab is hot-rolled to produce a hot-rolled sheet. The hot-rolled sheet may have a thickness of 1.0 to 4.5 mm. In one embodiment of the present invention, a preliminary cold-rolling step may be additionally included before cold rolling, so that even if the hot-rolled sheet is relatively thick, a non-oriented electrical steel sheet of an appropriate thickness can be produced. More specifically, the thickness of the hot-rolled sheet may be 1.5 to 3.5 mm.

[0128] The step of manufacturing the hot rolled sheet may include a step of finish rolling at a temperature of 850°C or higher.

[0129] If the hot rolling finishing temperature is too low, the rolling load increases, which reduces the hot rolling workability. In addition, a lot of deformation structures remain in the hot rolled steel sheet, which can cause an increase in the rolling load during the subsequent preliminary cold rolling process. In addition, during the intermediate annealing, deformation structures are removed. <111> / ND The recrystallization of the orientation grains is promoted, resulting in a lower magnetic flux density. Therefore, the higher the hot rolling finishing temperature, the better, and more specifically, finishing rolling at a temperature of 860 to 1000°C is preferable.

[0130] The step of manufacturing a hot-rolled sheet may include a step of performing water cooling after a time of 0.1 seconds or more after finish rolling.

[0131] After the finishing rolling, cooling is performed for coiling. When water cooling is performed immediately after the finishing rolling (i.e., within less than 0.1 seconds), the steel sheet may be rapidly cooled, causing deformation and residual stress, making coiling difficult. In addition, in terms of microstructure, the deformation stress after the finishing rolling is not released and remains, causing an increase in the rolling load and micro-stress in the subsequent cold rolling stage. <111> / ND may cause recrystallization of the orientation. Therefore, it is necessary to maintain the hot-rolled deformation structure for more than 0.1 seconds immediately after the hot-rolled finishing rolling to allow recovery and recrystallization, thereby reducing the rolling load during the subsequent preliminary cold rolling. <111> / ND suppresses the formation of azimuth recrystallization grains. More specifically, water cooling can be performed after 0.3 to 5.0 seconds, and even more specifically, water cooling can be performed after 0.5 to 3.0 seconds.

[0132] The step of manufacturing a hot rolled sheet may include a coiling step at a temperature of 600 to 800°C. A rough rolling step may also be included before the finish rolling step.

[0133] If the temperature during the coiling stage is controlled too low, the recovery and recrystallization of the hot-rolled deformation structure will not occur well, and the cooling load will increase to quickly cool the steel sheet to a low temperature, which may make it difficult to coil the supercooled coil. On the other hand, if the temperature is too high, recovery and recrystallization may be promoted, but additional oxidation by atmospheric oxygen may occur during coiling, which may cause thicker scale formation and the problem of intergranular oxidation. Intergranular oxidation of hot-rolled sheets promotes intergranular corrosion during the subsequent pickling process, which increases the possibility of surface stripe defects and may cause severe wear of the rolling rolls. Therefore, it is recommended that the coiling temperature be 600 to 800℃, and more specifically, coiling can be performed at 600 to 750℃.

[0134] After manufacturing a hot-rolled steel sheet, subsequent steps can be performed while the scale remaining on the hot-rolled steel sheet remains. That is, after hot rolling, scale removal processes such as pickling, shot blasting, or surface grinding can be omitted, and subsequent steps can be performed. By performing cold rolling without the pickling process, friction between the rolling work rolls and the steel sheet increases, so that shear deformation is simultaneously applied in addition to plane deformation during rolling, and a specific orientation develops during recrystallization annealing. In one embodiment of the present invention, scale refers to a portion on the surface of the steel sheet where elements such as Fe, Al, and Si combine with oxygen to form a phase different from that of the base metal. Remaining scale means that at least 1 μm of scale remains on the hot-rolled sheet. In this case, the scale thickness refers to the sum of the scale thicknesses formed on both surfaces of the steel sheet. If the remaining scale thickness is too thin, the effect due to the scale residue may not be fully exerted. Even if the scale thickness is thicker, the effect is not improved, and there is a problem of a reduced yield of the steel sheet. More specifically, scales with a thickness of 0.1 to 1 μm may remain.

[0135] In one embodiment of the present invention, after manufacturing a hot-rolled steel sheet, a pre-cold rolling annealing step for annealing the hot-rolled steel sheet may be performed immediately. Alternatively, a pre-cold rolling annealing step for annealing the pre-cold rolled steel sheet may be performed after performing preliminary cold rolling on the hot-rolled steel sheet.

[0136] Preliminary cold rolling is distinguished from cold rolling, which will be described later, in that it is the first rolling stage of the process of rolling to an intermediate thickness rather than the final product thickness, then performing intermediate annealing, and then cold rolling to the final product thickness.

[0137] Preliminary cold rolling can be performed at a reduction ratio of 65 to 80% to improve final cold rolling productivity and grain size in the final product sheet. Furthermore, if rolling productivity is not a consideration, the present invention also allows preliminary cold rolling to be performed in a reverse mill. The preliminarily cold rolled sheet can have a thickness of 0.3 to 1.5 mm. More specifically, the reduction ratio can be 68 to 78% and the thickness can be 0.6 to 1.3 mm.

[0138] The preliminary cold rolling reduction can be calculated as (steel thickness before rolling - steel thickness after rolling) / steel thickness before rolling. If the reduction ratio is too low in the preliminary cold rolling stage, the rolling load increases during the final cold rolling, which reduces productivity and increases the final reduction ratio, which causes fine grains. <111> / ND This can lead to problems that promote directional recrystallization. Conversely, if the reduction ratio is too high, the cold rolling load increases and the possibility of plate fracture increases.

[0139] The pre-cold rolling step can be performed at a temperature of 60 to 300°C. This temperature can be raised naturally by friction between the steel sheet and the rolling rolls, or by external heating. If the temperature is too low, the rolling load increases significantly, and the steel sheet may slip between the rolling rolls instead of being rolled, resulting in problems such as twisting. If the temperature is too high, a thick oxide layer may form on the steel sheet surface, which can deteriorate magnetism and cause problems such as ignition of the rolling oil. More specifically, it is preferably performed at a temperature of 70 to 250°C. The aforementioned temperature refers to the temperature of the steel sheet.

[0140] As mentioned above, the preliminary cold rolling step can be omitted if necessary.

[0141] Next, in the annealing step before cold rolling, hot-rolled steel sheets or preliminary cold-rolled sheets are annealed.

[0142] The soaking temperature during the annealing stage prior to cold rolling can range from 800 to 1200°C. If the annealing temperature is too low, recrystallized structures may not form or grow finely, resulting in a small increase in magnetic flux density. If the annealing temperature is too high, magnetic properties may deteriorate, and deformation of the plate shape may deteriorate rolling workability. More specifically, the temperature range may be 830 to 1170°C. The soaking time may range from 15 to 180 seconds.

[0143] In one embodiment of the present invention, the size distribution and density of carbides can be controlled by controlling the cooling pattern in the annealing step prior to cold rolling.

[0144] Figure 1 schematically illustrates the cooling pattern in the annealing stage prior to cold rolling.

[0145] As shown in Fig. 1, the step of cracking the steel plate includes: a first cooling step (C1) of cooling the steel plate to a first cooling temperature (T1) at a first cooling rate; and a second cooling step (C2) of cooling the steel plate to a second cooling temperature at a second cooling rate (T2) that is 3 to 17°C / sec higher than the first cooling rate.

[0146] The first cooling step (C1) cools the steel plate from the soaking temperature (T0) to the first cooling temperature (T1) at a first cooling rate. In one embodiment of the present invention, the cooling temperature in the cooling step refers to the average cooling temperature over the entire time of the cold step. In Fig. 1, the cooling rate is expressed as being uniform, but it may vary over time.

[0147] The first cooling temperature (T1) may be 580 to 770°C. If the first cooling temperature (T1) is too low, it means that cooling was performed at the first cooling rate for a long time, and at this time, the magnetic flux density and iron loss may deteriorate due to deformation of the material caused by thermal shock and residual stress resulting therefrom. If the first cooling temperature (T1) is too high, the first cooling step (C1) may be terminated prematurely, forming fine carbides, which may cause problems in terms of the magnetic flux density and iron loss. In one embodiment of the present invention, the cooling temperature is based on the plate surface temperature. More specifically, the first cooling temperature (T1) may be 600 to 750°C.

[0148] The first cooling rate may be 5 to 20°C / sec. If the first cooling rate is too slow, the carbide may coarsen, which may lead to problems in terms of grain growth inhibition and magnetic deterioration. If the first cooling rate is too fast, problems in terms of residual stress due to thermal shock may arise. More specifically, the first cooling rate may be 10 to 15°C / sec.

[0149] Next, the second cooling step (C2) cools from the first cooling temperature (T1) to the second cooling temperature (T2) at a second cooling rate. At this time, the second cooling rate is 3 to 17°C / sec higher than the first cooling rate. If the difference between the second cooling rate and the first cooling rate is small, problems may arise in that the overall annealing time increases and carbide growth is promoted. If the difference between the second cooling rate and the first cooling rate is too large, problems may arise in that magnetic deterioration occurs due to residual stress formed by rapid cooling. More specifically, the second cooling rate may be 5 to 15°C / sec higher than the first cooling rate.

[0150] The second cooling temperature (T2) may be 280 to 370°C. If the second cooling temperature (T2) is too low, it means that cooling at the second cooling rate is performed for a long time, which may cause problems in terms of an increase in the amount of carbide precipitation. If the second cooling temperature (T2) is too high, the second cooling step (C2) may be terminated prematurely, which may cause problems in terms of insufficient time for the growth of fine carbides. More specifically, the second cooling temperature (T2) may be 300 to 350°C.

[0151] The second cooling rate may be 10 to 30°C / sec. If the second cooling rate is too slow, carbide precipitation may increase significantly. If the second cooling rate is too fast, residual stress due to rapid cooling may increase. More specifically, the second cooling rate may be 15 to 25°C / sec.

[0152] After the second cooling step, cooling to room temperature is possible, but additional cooling and insulation may be performed to prevent plate breakage due to material deviation in the width and length directions and shape defects when cooling to room temperature.

[0153] The aforementioned pre-cold rolling annealing can be performed in vertical continuous annealing equipment or horizontal continuous annealing equipment. When performing annealing, a pickling process can be performed to remove any oxide layer that may exist on the steel sheet before annealing using sulfuric acid, hydrochloric acid, or nitric acid. Alternatively, pickling can be performed after annealing to remove any oxide layer remaining on the surface.

[0154] Returning to the description of the method for manufacturing non-oriented electrical steel sheets, cold-rolled sheets are manufactured by cold-rolling an annealed steel sheet. At this time, cold rolling can be performed at a reduction ratio of 30 to 80%. If the reduction ratio is too low, the accumulated strain energy in the rolled steel sheet is small, making it difficult to recrystallize in the subsequent annealing process, and the rolled structure remains, which can cause problems in improving the magnetic flux density and iron loss. On the other hand, if the reduction ratio is too high, it can cause problems in the subsequent annealing process. <111> / ND The recrystallization of the orientation grains is promoted and the grains become finer, which may cause problems such as poor magnetic flux density and increased iron loss. More specifically, the reduction ratio can be 40 to 70%. The thickness can be 0.1 mm to 0.5 mm. More specifically, it can be 0.15 to 0.35 mm. The cold rolling step can use a tandem cold rolling mill that continuously cold rolls the steel sheet using multiple rolling stands, or a reverse rolling mill that discontinuously cold rolls using 12 or more rolling rolls.

[0155] Next, the step of annealing the cold rolled sheet can be performed at a temperature range of 600 to 1200℃. If the annealing temperature is too low, <111> / ND orientation grains are accelerated for recrystallization, and the grains become finer, making it difficult to secure excellent magnetic flux density characteristics. If the annealing temperature is too high, the grains grow coarsely, increasing iron loss. In addition, an oxide or nitride layer may form on the steel sheet surface from the annealing atmosphere gas, which also increases iron loss. More specifically, annealing can be performed at 750 to 1100°C.

[0156] After the cold-rolled sheet annealing step, a step of forming an insulating film may be further included to ensure insulation and corrosion resistance of the steel sheet. Since the insulating film is widely known, a detailed description thereof will be omitted.

[0157]

[0158] The present invention will be described in more detail below through examples. However, these examples are intended only to illustrate the present invention and are not intended to limit the present invention.

[0159]

[0160] Example 1

[0161] A slab was manufactured with the composition shown in Table 1 below. The remainder is Fe. The slab was heated to 1150°C, hot-finish rolled at 920°C, and coiled at 650°C to produce a 2.3 mm hot-rolled sheet. Subsequently, the hot-rolled sheet was preliminarily cold-rolled to 1.5 mm. Subsequently, the slab was soaked to 1100°C for 30 seconds, then cooled to 600°C at a cooling rate of 10°C / sec, cooled to 350°C at a cooling rate of 15°C / sec, and then air-cooled to room temperature. Subsequently, the final cold-rolling was performed using a reverse rolling mill to a thickness of 0.25 mmt, annealed at 900°C for 100 seconds, and then applied with an insulation coating. The carbides in the steel sheet were measured by TEM and EDS and are summarized in Table 2 below.

[0162] The magnetic properties were measured using an Epstein tester by preparing Epstein specimens at each angle, and the results are summarized in Table 2 below.

[0163] The magnetic flux density and iron loss were expressed as average values ​​in the rolling direction and the direction perpendicular to the rolling.

[0164]

[0165] No.Si (wt%)Al(wt%)Mn(wt%)C(ppm)S(ppm)N(ppm)Ti(ppm)Mo(ppm)V(ppm)Nb(ppm)A12.701.60.770141616155012A22.701.6 0.732155515201215A32.701.60.7282021201535135A42.701.60.7166232294012550A52.701.60.7202326315010720A 62.701.60.7251017243015415B13.450.71.25616325885--B23.450.71.228222826--70B33.450.71.226162314-125- B43.450.71.220152722-10040B53.450.71.23023262310-80B63.450.71.2451520327020-B73.450.71.245152032555

[0166] No. Carbide density (units / ㎛2) 20 nm or more Mo, V, Nb Carbide ratio B50 (T) W10 / 400 (W / kg) Remarks A1 3.25 0.15 1.58 13.6 Comparative example A2 2.42 0.10 1.59 13.7 Comparative example A3 3.70 0.35 1.57 13.9 Comparative example A4 2.80 0.16 1.58 13.8 Comparative example A5 2.31 0.24 1.63 12.9 Example A6 2.45 0.23 1.62 13.4 Example Example B12.610.181.5714.1Comparative Example B22.830.131.5813.9Comparative Example B32.720.151.5814.0Comparative Example B42.430.271.6113.2Embodiment B52.350.261.6113.3Embodiment B62.380.241.6213.0Embodiment B72.620.091.5913.9Comparative Example

[0167] As shown in Tables 1 and 2, it can be confirmed that the examples in which the steel components are appropriately controlled, the process conditions are appropriately controlled, and carbides are appropriately formed have excellent iron loss and magnetic flux density.

[0168] On the other hand, if the steel component is not properly controlled, carbides are not properly formed, and it can be confirmed that the iron loss and magnetic flux density are inferior.

[0169]

[0170] Example 2

[0171] A slab containing Si: 3.5%, Al: 0.8%, Mn: 1.8%, C: 0.0025%, S: 0.0020%, N: 0.002%, Ti: 0.003%, Mo: 0.007%, V: 0.003%, Nb: 0.004% and the remainder Fe in wt% was heated to 1100℃ and then hot-rolled to a thickness of 1.5 mmt. The hot-rolled sheet was annealed under the conditions shown in Table 3 below, and then finally cold-rolled using a tandem rolling mill with multiple rolling stands to a thickness of 0.20 mmt, maintained at a temperature of 950℃ for 100 seconds, cooled, and then subjected to insulation coating treatment.

[0172] The magnetic properties and carbide analysis of the final product were performed in the same manner as in Example 1 and are shown in Tables 3 and 4.

[0173] No. Cracking temperature (℃) First cooling rate (℃ / s) First cooling temperature (℃) Second cooling rate (℃ / s) Second cooling temperature (℃) C1 1000 10600 15350 C2 1000 25600 15350 C3 900 10550 15350 C4 1000 10800 15320 C5 900 10600 15320 C6 1000 15600 15320 C7 850 5650 15300 C8 900 10700 20320 C9 950 15750 25350 C10 1000 5650 15300 C1 1 050 10700 20320 C1 2 850 10750 30350 C1 3 900 20650 22300

[0174] No. Carbide density (pieces / ㎛) 2)Mo, V, Nb carbide ratio of 20 nm or moreB50(T)W10 / 400(W / kg)RemarksC12.400.211.6113.2ExampleC22.830.131.5813.8ComparativeExampleC32.720.151.5813.9ComparativeExampleC42.430.181.5813.8ComparativeExampleC52.350.261.6113.1ExampleC62.380.191.5913.7ComparativeExampleC 72.310.231.6313.0 Example C82.400.211.6213.2 Example C92.420.221.6113.3 Example C102.340.251.6213.2 Example C112.380.231.6213.2 Example C122.430.161.5813.9 Comparative Example C132.600.211.5914.0 Comparative Example

[0175] As shown in Tables 3 and 4, when the cooling pattern is appropriately controlled during the annealing process prior to cold rolling, carbide properties are appropriately controlled, resulting in excellent magnetic properties. Conversely, when the cooling pattern is not appropriately controlled, numerous carbides or micro-carbides are generated, resulting in inferior magnetic properties.

[0176]

[0177] The present invention is not limited to the embodiments described herein, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Containing Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%, the remainder being Fe and inevitable impurities. A non-oriented electrical steel sheet having a carbide count ratio of 0.2 or more, with respect to the total number of carbides in the steel sheet, and having a particle size of 20 nm or more and containing 5 wt% or more of at least one of Mo, V, and Nb. In the first paragraph, The density of the above carbide is 2.5 / ㎛ 2 Below is the non-oriented electrical steel sheet. In the first paragraph, Non-oriented electrical steel sheet further comprising at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%). In the first paragraph, A non-oriented electrical steel sheet further comprising 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge and As. In the first paragraph, A non-oriented electrical steel sheet further comprising at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%). In the first paragraph, B: Non-oriented electrical steel sheet further comprising at least one of: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%). A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%, with the remainder being Fe and unavoidable impurities; An annealing step prior to cold rolling to anneal the above steel plate; A step for manufacturing cold rolled steel sheets by cold rolling an annealed steel sheet, and A cold rolled sheet annealing step for annealing the above cold rolled sheet; Including, The annealing step before the above cold rolling A step of cracking the above steel plate; A first cooling step of cooling the steel plate to a first cooling temperature at a first cooling rate; and A method for manufacturing a non-oriented electrical steel sheet, comprising a second cooling step of cooling the steel sheet to a second cooling temperature at a second cooling rate that is 3 to 17°C / sec higher than the first cooling rate. In Article 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%). In Article 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further contains 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge and As. In Article 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%). In Article 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of B: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%). In Article 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the subsequent steps are performed while the scale remaining on the hot-rolled steel sheet remains after manufacturing the hot-rolled steel sheet. In Article 7, A method for manufacturing a non-oriented electrical steel sheet further comprising a step of preliminarily cold rolling a hot-rolled sheet prior to the above-mentioned pre-cold rolling annealing step. In Article 13, A method for manufacturing a non-oriented electrical steel sheet having a reduction ratio of 65 to 80% in the above preliminary cold rolling step. In Article 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the cracking temperature in the annealing step prior to the above cold rolling is 800 to 1200°C. In Article 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the first cooling temperature is 580 to 770°C. In Article 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the second cooling temperature is 280 to 370°C. In Article 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the first cooling rate is 5 to 20°C / sec and the second cooling rate is 10 to 30°C / sec.

Images